Mobile operator

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _03_MobileOperator
{
    class Program
    {
        static void Main(string[] args)
        {
            string time = Console.ReadLine().ToLower();
            string contract = Console.ReadLine().ToLower();
            string internet = Console.ReadLine().ToLower();
            int months = int.Parse(Console.ReadLine());
            double sum = 0.0;

            if (time == "one")
            {
                switch (contract)
                {
                    case "small":
                        sum += 9.98;
                        break;
                    case "middle":
                        sum += 18.99;
                        break;
                    case "large":
                        sum += 25.98;
                        break;
                    case "extralarge":
                        sum += 35.99;
                        break;
                }
                if (internet == "yes")
                {
                    if (sum <= 10.00)
                    {
                        sum += 5.50;
                    }
                    else if (sum > 10 && sum <= 30.00)
                    {
                        sum += 4.35;
                    }
                    else
                    {
                        sum += 3.85;
                    }
                }
            }
            else
            {
                switch (contract)
                {
                    case "small":
                        sum += 8.58;
                        break;
                    case "middle":
                        sum += 17.09;
                        break;
                    case "large":
                        sum += 23.59;
                        break;
                    case "extralarge":
                        sum += 31.79;
                        break;
                }
                if (internet == "yes")
                {
                    if (sum <= 10.00)
                    {
                        sum += 5.50;
                    }
                    else if (sum > 10 && sum <= 30.00)
                    {
                        sum += 4.35;
                    }
                    else
                    {
                        sum += 3.85;
                    }
                }
                sum -= sum * 0.0375;
            }
            sum *= months;
            Console.WriteLine($"{sum:F2} lv.");
        }
    }
}